This invention relates to fluorescent lighting systems and, more particularly, to an efficient, low cost power supply for a fluorescent lamp.
Fluorescent lamps are generally regarded as being superior to incandescent lamps in a number of respects, including the quality of the light, the efficiency of conversion of electrical power to light power, and lamp life. The principal drawbacks of fluorescent lamps in the past have been the initial high cost of lamp fixtures and electrical control circuitry, and the difficulty of adapting conventional incandescent lamp installations to accept fluorescent lamps. These drawbacks have in large measure been eliminated by the commercial availability of so-called circline fluorescent lamps and adapters therefor. Circline lamps are annular in form, generally having a 61/2 or eight inch diameter, and have a so-called rapid start capability, i.e., the two electrodes each have a pair of terminals across which an electrical potential is applied to heat the electrode while starting the lamp. As a result, the expensive electrical control circuitry required to provide the high starting voltage is avoided. Fixtures having a screw base for adapting circline lamps to incandescent lamp sockets, and fixtures having mounting sleeves for adapting circline lamps to table lamp pedestals have recently been introduced to consumers.
Conventionally, circline lamps and straight, rapid start fluorescent lamps are started by connecting the two terminals of each electrode in series with a heat activated, normally closed switch and this lamp-switch configuration in series with a suitable inductor across the source of line voltage. After a short period of time, sufficient to heat the electrodes, the switch opens to impress the line voltage plus spike voltage from the inductor between the electrodes, which starts the lamp.